This invention relates generally to coffee-makers of the paper filter type and more particularly to a free-standing coffee-maker assembly which has a large maximum capacity and yet is capable of effectively brewing coffee within a broad operating range.
Coffee-makers are known which are of the so-called pour-over paper-filter type. One such maker on the market is the Silex coffeebrewer which is disclosed in Silex U.S. Pat. No. Des. 201,949, the maker including a stand serving to raise a water reservoir above a funnel functioning as a brewing chamber below which is placed a coffee decanter.
In the Silex coffee-maker, a bed of ground coffee is formed in a disposable paper filter nested within the funnel, boiling water contained in the reservoir being discharged through a nozzle which is adapted to spray the water so that it is distributed over the entire bed of coffee grounds. The brewed beverage resulting from the infusion process which takes place in the brewing chamber is fed into the coffee decanter.
The throw-away paper filter nested within the funnel in the Silex coffee-maker has a frusto-conical form, with a pleated wall and a flat base to provide a large filtering area. In the coffee-maker disclosed in the Martin U.S. Pat. No. 3,374,897, use is made of a similarly-shaped paper filter and a stand-supported funnel; but to physically separate the flat base of the filter from the bottom of the funnel, the funnel bottom includes upstanding radial ribs to define a space below the filter permitting the free flow of the coffee extract to a central discharge port.
The maximum capacity of a coffee-maker of the type shown in the Silex and Martin patents is fixed by the size of the brew basket or funnel and the complementary size of the paper filter; for these sizes determine the volume of ground coffee that can be contained therein. If, therefore, the parameters of the funnel and filter are such as to provide the coffee-maker with a 12-cup capacity, this amount of coffee extract will be produced when the volume of ground coffee in the basket is sufficient for this purpose and an adequate amount of water is poured over the ground coffee bed.
The boiling water sprayed on the bed of ground coffee percolates through the bed in a single pass, the rate of percolation being determined by the volume and grind of the ground coffee and the flow characteristics of the filter. Thus for a given grind, the greater the volume of the ground coffee bed, the slower is the rate of percolation and the greater the infusion action. In practice, these variables are chosen to provide for a given rated coffee-maker capacity a coffee extract of acceptable quality. However, with known coffee makers of the paper filter type, the maker is incapable of functioning effectively when used to produce an amount of brewed coffee much below the rates maximum capacity of the maker.
Thus while a 12-cup capacity coffee-maker will also function effectively to produce 10 cups, in that the volume of ground coffee for a 10-cup output is not much less than for a 12-cup output, if one tries to use the same maker to brew, say, only four or five cups of coffee, then the resultant coffee extract will be weak or of poor quality. The reason for this is that to produce a four-cup output, one must use a relatively small volume of ground coffee, as a result of which the water percolates through the bed at too rapid a rate and proper infusion is not obtained.
In the typical household, it is the practice to purchase a coffee-maker which is suitable for the largest anticipated requirement, say, a party of 10 or 12. Since on most occasions the actual demand for coffee is limited to the number of people who make up the household, which is rarely greater than six, a large capacity coffee-maker of the type heretofore known has limited utility; for its use is reserved for those relatively rare occasions which call for the full capacity of the maker. For everyday use, the householder must therefore purchase a small capacity coffee-maker which operates in, say, the three-to-five-cup range.